Use JavaRef in JNI generator sample.

base/android/jni_generator/sample_for_tests.cc

Index: base/android/jni_generator/sample_for_tests.cc
diff --git a/base/android/jni_generator/sample_for_tests.cc b/base/android/jni_generator/sample_for_tests.cc
index 157b7cd86af881ede7742671f7d023bfaf4c4a70..42b2143e9898fb22a0454e07c00a48e5179d11c7 100644
--- a/base/android/jni_generator/sample_for_tests.cc
+++ b/base/android/jni_generator/sample_for_tests.cc
@@ -117,7 +117,7 @@ int main() {
 
   // This is how you call a java method from C++. Note that you must have
   // obtained the jobject somehow.
-  jobject my_java_object = NULL;
+  ScopedJavaLocalRef<jobject> my_java_object;
   int bar = base::android::Java_SampleForTests_javaMethod(
       env, my_java_object, 1, 2);